Precipitation/hail sensor and method for precipitation rate measurement

ABSTRACT

The invention relates to a precipitation detector ( 1 ) and method for measurement of precipitation parameters. The detector ( 1 ) includes a frame ( 5 ), a surface ( 2 ) mounted on the frame ( 5 ) and adapted to receive hydrometeors, and detection means ( 3 ) for converting the impact impulses of hydrometeors into an electric signal. According to the invention, the surface ( 2 ) receiving the impact of the hydrometeors is convex, stiff and rigidly connected to the detector frame ( 4 ) with the detection means ( 3 ) being permanently connected to the surface ( 2 ) receiving the impact of the hydrometeors.

The invention relates to a precipitation/hail detector according to thepreamble of claim 1.

The invention also relates to a method for precipitation ratemeasurement.

Rain detectors conventionally used in the art can be categorized in twogroups:

-   -   1) Collector-type rain gauges in which rainwater is collected        into a collection vessel and the amount of water accumulated        therein is measured by weighing the mass of the collected        rainwater or by detecting the level of collected rainwater.    -   2) Precipitation rate type detectors comprising a funnel-like        collector with a small-volume vessel placed thereunder. The        vessel is arranged to empty itself automatically when a        predetermined amount of water is accumulated therein (the        simplest implementation being a tipping-bucket mechanism). The        detector delivers a count pulse every time the bucket empties        itself, whereby one pulse is calibrated to represent a        predetermined amount of rain, e.g., 0.1 mm.

These types of precipitation rate rain detectors are hampered by thefollowing problems:

-   -   The emptying of the collection vessel causes additional manwork        (in manual emptying) or dead time in the measurement cycle (in        automatic emptying).    -   The collection vessel or funnel also easily catches dirt        requiring scheduled cleaning of the vessel or funnel.    -   Adherence of rainwater on the rims of the collection vessel        and/or evaporation of rainwater from the collecting vessel cause        significant measurement errors.    -   Moving parts of the rain detector may jam due to soiling or,        e.g., insects entering the detector structures.

Whilst operating on a different principle, a piece of equipment calledthe distrometer may also be used for measuring precipitation rate.Distrometer is a device capable of measuring the droplet sizedistribution in precipitation. This kind of mechanical distrometer(so-called Joss-Waldvogel rainfall distrometer) includes a conicaldetector plate that is springedly supported on the device frame so thatdroplets falling thereon can deflect the plate from its equilibriumposition. The movement of the detector plate is measured inductively bya sensor coil. Voltage pulses generated in the sensor coil due to theraindrop impacts are registered and, on the basis of pulse magnitude andempirical calibration coefficients, the masses and size distribution ofindividual droplets are computed. The raindrop distribution function mayfurther be analyzed to compute the intensity and accumulative totalamount of precipitation. Due to its expensive and complicatedconstruction a distrometer is not generally used as all-round raindetector, but rather, only in meteorological research for measuring thesize distribution of raindrops. The complex structure of the system ischiefly due to the springed mounting of the conical detector plate tothe distrometer frame and awkward measurement method dictated by thisclumsy mechanical construction with its force feedback arrangement.

Internet page document http://www.sensit.com/rain.htm describes a devicefor measuring the kinetic energy of raindrops. This measurement devicehas two pulse outputs that indicate:

-   1) the number of raindrops (output pulse is delivered if the    detected energy signal exceeds a predetermined limit value) and-   2) the kinetic energy of raindrops computed by integrating the    output signal of the piezoelectric sensor of the device.

Either one of these variables is dependent on both the mass and thevelocity of the rain drop thus not being directly suitable for use as arainfall rate indicator. Furthermore, the above-mentioned device doesnot incorporate any computational intelligence inasmuch as it isimplemented using discrete components alone.

It is an object of the present invention to provide a novel type of raindetector capable of overcoming the problems of the prior-art technologydescribed in the foregoing.

The invention is based on the concept of detecting rainfall and its typeby means of an acceleration or force sensor that is rigidly mounted onthe device case. Respectively, the method according to the invention isbased on analyzing the output signal obtained from the force sensor asto the shape of output signal pulse generated by each raindrop or hailparticle individually thus being capable of determining the volume ofthe impinging raindrop or counting the number of raindrops per time unitor, alternatively, categorizing the rainfall as hails. The total amountand intensity of rain is then determined from the measurement data ofthe individual raindrops or counted number of raindrop impacts per timeunit. The computational algorithm disclosed herein may be carried outusing only the raindrop count data or only the data representing theraindrop size parameter values or both.

Furthermore, also the raindrop size distribution may be determined fromthe measurement data recorded individually for each raindrop.

According to the invention, wind-related error in the amount andintensity of rain may be corrected with the help of a separate winderror correction algorithm.

The invention is further characterized in that one or morecharacteristic parameters, which is/are dependent on the size of one ormore raindrops in the signal representing the overall amount ofraindrops and/or a single raindrop, is/are used for compiling a signalparameter that is proportional to the total volume of the detectedraindrops, whereby the summing of the latter signal parameter valuesmakes it possible to compute the total amount and intensity of detectedrainfall.

According to a preferred embodiment of the invention, the parametercomputation is integrated with the detector construction so that itsoutput signal is directly proportional to the total amount and/orintensity of precipitation.

More specifically, the precipitation detector according to the inventionis characterized by what is stated in the characterizing part of claim1.

Furthermore, the method according to the invention is characterized bywhat is stated in the characterizing part of claim 11.

The invention offers significant benefits.

Firstly, the precipitation detector according to the invention is freefrom any moving parts. In its basic version, the detector has nocollection vessel or funnel needing emptying or cleaning, no cloggingparts or propensity to error due to adherence or evaporation ofcollected rainwater. Whilst operating in the same principle as amechanical distrometer, the detector features a very simple and costefficient construction.

Secondly, the detector according to the invention uses only a singlesensor system to detect, not only the total amount of rainfall, but alsorainfall intensity and to identify hails in precipitation.

A preferred embodiment of the invention facilitates compensation ofmeasurement errors due to wind

In the following, the invention will be examined with the help ofexemplifying embodiments illustrated in the appended drawings in which

FIG. 1 is an exploded view of a detector according to the invention;

FIG. 2 a is a longitudinally sectional side elevation view of a secondembodiment of a detector according to the invention;

FIG. 2 b is a longitudinally sectional top view of the detectorembodiment of FIG. 2 a;

FIG. 3 is a graph illustrating the impulse of a falling raindrop in asystem according to the invention;

FIG. 4 is a plot illustrating a calibration curve used in the invention;

FIG. 5 is a graph illustrating the impulse of a falling hail in a systemaccording to the invention;

FIG. 6 is a view of a precipitation detector according to the inventionequipped with a wind measurement device;

FIG. 7 is a graph illustrating the effect of wind on the precipitationmeasurement; and

FIG. 8 is a graph illustrating the outcome of wind correction in themeasurement results.

As mentioned above, the invention relates to the measurement of totalamount of precipitation, distribution of hydrometeor size and intensityof precipitation. Next, the definitions of these variables are givenbelow.

Total Amount of Rainfall (also called the cumulative rainfall)

Vertical height of rainfall column on a flat-bottom vessel. Standardunit is mm.

Rainfall Intensity

Total amount of rainfall per time unit. Standard unit is mm/h.

Raindrop Size Distribution

Number of raindrops in a given droplet size fraction suspended in unitvolume of air.

Accordingly, the goal in the measurement of total amount of rainfall isto determine the total volume of raindrops detected per horizontal unitarea.

Prior-art measurement technique of kinetic energy of raindrops is basedon summing the kinetic energies E=½ m v² of the individual raindrops.

Now referring to FIG. 1, the precipitation detector 1 shown thereincomprises a detector surface 2 whereon hydrometeors such as raindropsand/or hails impinge, a detector 3 serving to detect the energy pulsesof raindrops impinging on the detector surface 2, complemented withmeasurement electronic circuitry 4 and a computational algorithm that incombination are capable of computing rainfall intensity (mm/h) andcumulative rainfall (mm).

The detector surface 2, which acts as the impact-receiving surface forthe falling raindrops, is stiff and mounted on the detector case 5.Mounting may be made entirely rigid or implemented with the help of anO-ring or the like resilient mounting adapter component Typically,detector 3 is rigidly mounted on the detector surface 2. Computationutilizes information recorded on the number of registered raindroppulses and/or some other parameter of the detector output pulse known tobe dependent on the size of the impinging raindrop, such as the pulseamplitude or the full-width at half maximum (FWHM) value of the pulse ora combination of both.

The detector surface 2 is made planar, plate-like or convex (domed) andshaped so that accumulation of water thereon is impossible. To make themounting of detector 3 easier, its mounting area on the detector surface2 may be shaped planar. As a rule of design, the larger the area of thedetector surface the greater the number of raindrops impinging thereonand, hence, the smaller the statistical error in the computed value ofcumulative rainfall. On the other hand, a large area of the detectorsurface means that the number of raindrop impacts coinciding with eachother increases which means problems in the interpretation of themeasured signals. In practice, a good compromise for the detectorsurface area has been found to be 20 to 150 cm². The detector may alsobe comprised of multiple units, each one of them equipped with anindividual detector assembly.

Detector 3 senses the deformation caused by the impinging raindrops onthe detector surface. In a practicable construction, detector 3 may beimplemented using, e.g.,:

-   -   a force or acceleration sensor attached to the detector surface,        or    -   a pressure-sensitive film covering the detector surface, such as        piezoelectric PVDF polymer film or a layer of piezoelectric        ceramic material.

In an ideal case, the response of the system combination of the detectorsurface with the detector is such that the output pulse amplitude andwaveform are independent from the location of the raindrop impingementpoint, whereby the detector surface is homogenous. This is not crucialto the system function, because a nonuniform response only causes arandom error in the measurement signal that can be eliminated by using asufficiently long integration time.

The computation of cumulative rainfall and intensity thereof on thebasis of the signal information recorded for the individual pulses canbe implemented in plural different ways. Whilst the simplest techniqueis to count the number of raindrops only, the accuracy and reliabilityof detector response can be improved by way of additionally utilizingother information conveyed in the waveform of the detector output pulses(e.g., pulse amplitude or the half maximum pulse width). Herein,computation is advantageously carried out with the help of digitalsignal processing techniques and a microprocessor.

In FIGS. 2 a and 2 b is shown an alternative embodiment of detector 1 ofFIG. 1. The detector 1 is constructed into a cylindrical case, whosecover 2 is a slightly convex metal disc acting as the detector surfacemade from, e.g., 1 mm thick stainless sheet steel. The cover 2 isrigidly connected at its rim centrally on the detector case 5 andfurther has mounted by glueing or soldering on its underside apiezoelectric ceramic element 3. The piezoelectric element is a discmade from a piezoelectric ceramic material that is metallized on itsboth sides so that its two contact electrode areas are located on theopposite sides of the disc-like element In this application thepiezo-electric element 3 acts as a force sensor detecting the impacts ofhydrometeors. The electrodes of piezoelectric element 3 are connected toan electronic amplifier 4 that is located in the interior of thedetector case. The amplified measurement signal is taken to thecomputing means over a cable passing through the bottom 8 of thedetector case. Alternatively, the entire measurement and computingelectronics circuitry may be fitted into the device case, whereby thedetector output can be a digital or an analog signal representing thecumulative rainfall and/or the intensity of rainfall.

When hitting the detector surface 2, the raindrop inflicts thereon aforce that is further transmitted to the piezoelectric element 3 and issubsequently identified as a voltage pulse generated over the element.The material and dimensions of detector cover 2 are selected such thatthe resonant vibration evoked by the impacting raindrop is attenuatedrapidly. In this construction, the waveform of the output pulse is asshown in FIG. 3.

The voltage pulses delivered by piezoelectric element 3 are filtered,amplified and analyzed as to their selected parameters related to theraindrop size before storage in the memory of the processor systemperforming final computations.

A number of different techniques can be used for computing rainfallintensity and cumulative rainfall from the gathered measurement data.

Next, two feasible methods are described.

Method 1

Computation is carried out using a fixed measurement cycle timeincrement, typically selected to be in the range 1-10 minutes. Outputpulses detected during the measurement cycle are analyzed for parametersx_(j) (which may include the full-width at half maximum value of thepulse (w_(1/2)), the peak-to-peak voltage (V_(pp)), the overall numberof pulses or any other parameter characterizing the output pulse, or acombination of the selected parameters) and the analyzed values arestored in the processor memory. At the end of each measurement cycle, anestimate on the incremental value ΔP of cumulative rainfall detectedover the cycle may be computed using an equation:ΔP=f(m,x ₁₁ , . . . ,x _(1n) ,x _(2l) , . . . ,x _(2n) , . . . x _(ml) ,. . . ,x _(mn))  (1)where

-   m=number of raindrops detected during a measurement cycle-   n=number of pulse-character zig parameters used in computation, and-   x_(ij)=value of pulse parameter j in the output pulse detected for    raindrop i.

The values of j may be selected, e.g., as follows: 1=half-maximum pulsewidth (w_(1/2)), 2=peak-to-peak voltage (V_(pp)), 3=number of pulses,4=other parameter characteristic of the output pulse, 5=a combination ofthe aforementioned. The half-maximum pulse width value w_(1/2), of thepulse refers to the full-width at half maximum (FWHM) value of apositive pulse waveform (=½*V_(max)).

Function f represents the experimentally determined dependence of themeasured pulse parameters on the rainfall variables.

Cumulative rainfall P is obtained summing the incremental rainfallvalues of successively recorded measurement cycles. The averageintensity R of rainfall during a measurement cycle can be computed fromequation:R=ΔP/t  (2)

This method is particularly useful for simultaneous measurement of theamount and intensity of rainfall.

Method 2

In this method, computation is performed out in real time so that theprocess begins on the detection of the first raindrop. Each detectedraindrop is analyzed for parameters x_(j) (which may as shown in FIG. 3be the half-maximum pulse width w_(1/2), peak-to-peak voltage V_(pp),peak voltage V_(max), minimum voltage V_(min), number of pulses or anyother parameter characterizing the output pulse, or a combination of theselected parameters), whereupon the cumulative rainfall P is computedfrom equation:P=Σ _(i) [f(Δt _(i) ,x _(i1) , . . . ,x _(in))]  (3)where index i=1,2, . . . refers to the individual raindrops detectedduring the measurement cycle, Δt_(i) is the time interval between thedetected raindrop and the preceding one, and function f represents theexperimentally determined dependence of the measured pulse parameters onthe raindrop volume.

This method makes it easy to implement a detector with a pulse outputwherefrom a single pulse is delivered at the instant the amount ofcumulative rainfall has grown large enough to exceed a predeterminedthreshold. Then, the detector output is identical to prior-art raindetectors of the tipping-bucket type, whereby it can be connecteddirectly to data collection equipment most commonly used in weatherstation installations.

The accuracy of the rain detector and the computational method describedabove is crucially dependent on the detector calibration accuracy. Thecalibration parameters, that is, the constants in Eqs. (1) and (3) aredetermined experimentally by comparing the detector response with anaccurate reference detector under laboratory or actual field conditionsusing regression analysis tools, for instance. An example of suchcalibration data is shown in FIG. 4.

Detection of hails is important on airfields, for instance. A prior-artdevice for this purpose is a hail detector comprising a metal plate witha microphone placed thereunder. Hails are identified by the impingementsound they create. This type of hail detector is hampered by itssensitivity to ambient noise making it suitable for use only ascomplementary detector in optical measurement systems of ambient weatherconditions as is described in U.S. Pat. No. 5,528,224.

Next, a method is described suited for hail detection in a more reliablefashion and with reduced sensitivity to ambient noise. Hail detectionmay be incorporated as a supplementary feature to the above-describedrain detector or, alternatively, it may be utilized in the constructionof a detector intended for hail detection alone.

Distinguishing hails from raindrops is based on the fact that thedetector signals they produce are very different from each other. Theimpact of a solid object such as a hail on the detector surface iselastic, whereby firstly the rate-of-rise of the output pulse is fasterand, secondly, the pulse amplitude is higher than in a pulse generatedby a raindrop. The third difference is found in that the hail impactexcites the resonant frequencies of the domed detector cover 2,whereupon the domed cover 2 continues vibrate after the impact. Thedifferences between various hydrometeors become clearly evident bycomparing the detector output pulse of FIG. 5 generated by a solidhydrometeor particle with the detector output pulse waveform of FIG. 3generated by falling raindrop.

The above-described rain detector embodiment is not sensitive toair-borne noise inasmuch as the detector element, in contrast to ahail-sensing microphone, is not directly communicating with ambient air.

The identification of hails may thus be based on the detection of aselected characteristic parameter of the detector output signal, such asthe amplitude, rise time or resonant frequency, or a combination of suchparameters. By using a combination of plural such characterizingparameters, the reliability of measurements is increased and the numberof false detection results due to ambient noise are reduced.

Wind is a significant error factor in rain measurements performed usingunprotected detectors. Errors ranging from zero up to 30% have beenreported in the art. The magnitude of the wind-related error isdependent on the wind velocity, rain intensity and type ofprecipitation.

There have been proposed in the art a number of different kinds of errorcorrection methods for compensation of the wind-related error. In asystem performing the measurement of rainfall and wind datasimultaneously within a confined area, it is possible to reduce theeffect of wind error on the measured value of rainfall intensity byapplying a suitable correction algorithm.

However, all conventional systems utilize wind data that has beenmeasured at a site clearly remote the site of rain data measurement.This is because wind data is typically measured at a height of somemeters above the ground, while rain measurement typically takes placesubstantially at the ground level thus being removed by at least severalmeters from the wind sensor. Hence, the wind information to be utilizedfor wind-related error correction does not fully represent the actualwind condition at the rainfall measurement site. Furthermore, currentmethods do not operate in real time, but instead, information for winderror correction is obtained periodically delayed, typically beingavailable in monthly, weekly, daily or 12-hour periods.

Therefore, next is explained a method according to the invention that iscapable of overcoming the disadvantages of the prior art describedabove. The method is generally characterized by the steps outlinedbelow.

-   -   For wind error correction, an algorithm is used capable using        wind information gathered directly at the operating site of the        rainfall detector or at least in a close vicinity thereof. In        the context of this description, the term “close vicinity” must        be understood to mean a distance of less than one meter from the        rainfall detector. Advantageously, the distance is less than 30        cm, which means that the wind sensor may be readily integrated        into one and the same measurement system.    -   The algorithm has a freely selectable time scale, whereby also        real-time correction is possible.    -   The algorithm is suited for all rainfall sensor types        irrespective of their operating principle.

A general form of the wind error correction factor isk=Rtr/R=f(w,R)  (4)where Rtr is the actual amount of rainfall, k is the error correctionfactor, w is the wind velocity, R is the measured amount of rainfall andf is an experimentally determined function expressing the dependence ofthe error correction factor on wind velocity and rainfall intensity. Thetime scale of error correction is defined to be compatible with the timeinterval needed for computing the values of variables R and w in Eq.(4).

The corrected amount of rainfall is obtained by multiplying the measuredamount of rainfall by correction factor k. The same correction techniquecan be employed in conjunction with other detector constructions,whereby the character of function f(w,R) may obviously vary.

In practice, the dependence of the error correction factor on the amountof rainfall R and wind velocity w expressed by function f(w,R) isdetermined experimentally by using two similar rainfall detectors. Inthe test arrangement, one these detectors is placed in a site maximallyeffectively protected from wind, whereby its reading represents anamount of rainfall Rtr uncorrupted by the wind error. Alternatively, thevalue of Rtr may be measured using a different type of rainfall detectorprotected from wind. The other rainfall detector is placed in a sitesubject to wind and, hence, its rainfall reading R is corrupted by awind-related error. In a close vicinity of the latter rainfall detectoris placed a wind sensor that measures the wind velocity w. As a result,function f(w,R) written in Eq. (4) can be determined from the thusgathered experimental data using nonlinear regression analysis methods,for instance.

As illustrated in FIG. 6, the system comprises an ultrasonic windvelocity measurement system adapted about rainfall detector surfacearea. Typically, the system comprises three ultrasonictransmitter-receiver units 9 allowing the direction and strength of windvelocity to be determined on the basis of the sound propagation timesbetween the ultrasonic transmitter-receiver units 9. This technology isdescribed in more detail, e.g., in U.S. Pat. No. 5,343,744. Thus, thisnovel arrangement makes it possible to measure wind parameterspractically in the same position with rainfall detection. In contrast,conventional weather stations have the rainfall detector located closeto the ground level, while wind is measured at the height of severalmeters thus being remote in regard to the site of rainfall detection.Hence, the embodiment of the invention disclosed herein is characterizedin that the sites of wind and rain measurements are located as close toeach other as possible, whereby both of these weather variables aremeasured substantially in the same position. In lieu of the ultrasonicmethod, also other techniques may be employed for wind measurement,e.g., thermal methods based on sensing temperature at the distal ends ofelongated elements that are aligned substantially vertically, wherebythe end of the measuring element facing wind is typically at the lowesttemperature.

In FIG. 7 are shown correction factor curves for different wind velocityclasses. Each data point represents the amount of rainfall collectedduring a 10-minute measurement cycle. The correction curves are thenfitted on the experimentally gathered data using a nonlinear regressionanalysis method.

In FIG. 8 are shown respectively the corrected and uncorrectedcollective rainfall values for two rainfall detectors accumulated duringa 10-day measurement period. The detectors used in the experiment wereidentical with the exception that one of them was mounted two metersabove the ground thus being subjected to wind while the other one waslocated at the ground level in a site protected from the wind. Ascompared with the readings of the ground-level detector, the detectorplaced two meters above the ground was found to give readings in whichthe measured collective rainfall was systematically smaller due towind-related error. Hence, the readings of the detector placed aboveground need correction. Obviously, the correction algorithm discussedabove can be used for improving the measurement accuracy of detectorsmounted above the ground level.

The applications of the construction according to the invention may befurther widened by complementing the system with a collecting-type raindetector. Herein, the system comprises two identical detectors, one ofthem having a collection funnel placed thereabove. The detector with thefunnel could then provide rainfall information for low precipitationrates, too. This arrangement could also be employed for systemself-diagnostics, whereby clogging of the funnel, for instance, may berecognized during periods of high precipitation rate as a smallerrainfall reading of the clogged detector.

The funnel may be designed heatable. Then, a detector equipped with aheated funnel during a snowfall can provide information on the actualprecipitation rate and the water value of the snowfall.

1. A precipitation detector for measurement of precipitation parameters,the detector comprising: a frame, a substantially stiff surface mountedon the frame and adapted to receive hydrometeors, and detection meansfor converting the impact impulses of hydrometeors into an electricsignal, said surface receiving the impact of the hydrometeors beingrigidly connected at its rim on the frame and the surface being at leastpartially convex, and said detection means being permanently connectedto said surface receiving the impact of the hydrometeors.
 2. Theprecipitation detector of claim 1, wherein in the immediate vicinity ofthe precipitation receiving surface is adapted a wind measurementsystem.
 3. The precipitation detector of claim 1, wherein the number ofsensors in said wind measurement system is three.
 4. The precipitationdetector of claim 1, wherein said sensors are ultrasonic sensors capableof measuring the propagation delay of sound.
 5. The precipitationdetector of claim 1, wherein said wind sensors are thermal wind velocitysensors.
 6. The precipitation detector of claim 1, wherein saidprecipitation receiving surface is a domed stirface.
 7. Theprecipitation detector of claim 1, wherein the top surface of saidprecipitation receiving surface is planar.
 8. The precipitation detectorof claim 1, wherein above said precipitation receiving surface isadapted to a collection means such as a funnel.
 9. A precipitationdetector system, further comprising two detectors of the kind disclosedin claim 1, one of the detectors being equipped with a precipitationcollecting funnel.
 10. The system of claim 9, wherein the precipitationcollecting funnel is adapted to be heatable.
 11. A method for measuringthe parameters of precipitation, the method comprising the steps ofmeasuring precipitation at the level of individual hydrometeors,counting the number of hydrometeors, compiling precipitation rateinformation from the measurement data collected at the level ofindividual hydrometeors that are recorded from the elastic deformationof a detector surface under the impacts of said individual hydrometeors,and the signal parameter information of the individual impacts or thenumber thereof per time unit is used in the determination ofprecipitation intensity, total amount of precipitation or analysis ofhydrometeor size distribution in precipitation, wherein the hydrometeorsare received by a surface which is rigidly connected at its rim on theflame and the surface is at least partially convex.
 12. The method ofclaim 11, wherein each one of the individually recorded impact signalsis processed to compile at least one parameter or a combination ofparameters responsive to the size of said hydrometeor in order todetermine the precipitation intensity, total amount of precipitation orhydrometeor size distribution in precipitation.
 13. The method of claim11, wherein said deformation detection means is constructed into aseparate structure that is connected to the surface of the precipitationdetector.
 14. A method of measuring the parameters of precipitation, themethod comprising the steps of measuring precipitation at the level ofindividual hydrometeors, and compiling precipitation rate informationfrom the measurement data collected at the level of individualhydrometeors, wherein precipitation rate is measured utilizing theelastic deformation of a detector surface under the impact ofhydrometeors, and categorization of hydrometeors into hails is based onthe signal information related to the individual hydrometeors.
 15. Themethod of claim 14, wherein the defonnation detections means isconnected in an integrated fashion to the surface of the precipitationdetector.
 16. The method of claim 1, wherein wind is measured at leastsubstantially in the same position with the precipitation ratemeasurement system.
 17. The method of claim 1, wherein wind is measuredusing an ultrasonic technique.
 18. The method of claim 1, wherein windis measured using a thermal technique.
 19. The method of claim 1,wherein precipitation is measured using an at least substantiallysimilar detector equipped with a collecting funnel and the measurementresult is obtained as a combination of the data recorded by bothdetectors.
 20. A method for measuring the parameters of precipitation,the method serving to detect the precipitation intensity, total amountof precipitation or hydrometeor size distribution in precipitation,comprising the following steps: measuring the wind at leastsubstantially in the position with a precipitation measurement system;and correcting the detected value of precipitation intensity, totalamount of precipitation or hydrometeor size distribution inprecipitation on the basis of the measured wind velocity.
 21. The methodof claim 20, wherein said correction is made in real time.
 22. Themethod of claim 20, wherein said precipitation measurement is performedusing a precipitation detector, comprising; a frame, a substantiallystiff surface mounted on the flame and adapted to receive hydrometeors,and detection means for converting the impact impulses of hydrometeorsinto an electric signal, said surface receiving the impact of thehydrometeors being rigidly connected at its rim on the frame and thesurface being at least partially convex, and said detection means beingpermanently connected to said surface receiving the impact of thehydrometeors.